diff --git a/packages/react-native/ReactCommon/jsinspector-modern/tests/JsiIntegrationTest.cpp b/packages/react-native/ReactCommon/jsinspector-modern/tests/JsiIntegrationTest.cpp
new file mode 100644
index 00000000000..ed1fb11d234
--- /dev/null
+++ b/packages/react-native/ReactCommon/jsinspector-modern/tests/JsiIntegrationTest.cpp
@@ -0,0 +1,254 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <folly/executors/QueuedImmediateExecutor.h>
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+#include <jsinspector-modern/InspectorInterfaces.h>
+#include <jsinspector-modern/PageTarget.h>
+
+#include <memory>
+
+#include "FollyDynamicMatchers.h"
+#include "InspectorMocks.h"
+#include "UniquePtrFactory.h"
+#include "engines/JsiIntegrationTestGenericEngineAdapter.h"
+#include "engines/JsiIntegrationTestHermesEngineAdapter.h"
+
+using namespace ::testing;
+
+namespace facebook::react::jsinspector_modern {
+
+namespace {
+
+/**
+ * A text fixture class for the integration between the modern RN CDP backend
+ * and a JSI engine, mocking out the rest of RN. For simplicity, everything is
+ * single-threaded and "async" work is actually done through a queued immediate
+ * executor ( = run immediately and finish all queued sub-tasks before
+ * returning).
+ *
+ * The main limitation of the simpler threading model is that we can't cover
+ * breakpoints etc - since pausing during JS execution would prevent the test
+ * from making progress. Such functionality is better suited for a full RN+CDP
+ * integration test (using RN's own thread management) as well as for each
+ * engine's unit tests.
+ *
+ * \tparam EngineAdapter An adapter class that implements RuntimeTargetDelegate
+ * for a particular engine, plus exposes access to a RuntimeExecutor (based on
+ * the provided folly::Executor) and the corresponding jsi::Runtime.
+ */
+template <typename EngineAdapter>
+class JsiIntegrationPortableTest : public Test, private PageTargetDelegate {
+  folly::QueuedImmediateExecutor immediateExecutor_;
+
+ protected:
+  JsiIntegrationPortableTest() : engineAdapter_{immediateExecutor_} {
+    instance_ = &page_->registerInstance(instanceTargetDelegate_);
+    runtimeTarget_ = &instance_->registerRuntime(
+        engineAdapter_, engineAdapter_.getRuntimeExecutor());
+  }
+
+  ~JsiIntegrationPortableTest() override {
+    toPage_.reset();
+    if (runtimeTarget_) {
+      EXPECT_TRUE(instance_);
+      instance_->unregisterRuntime(*runtimeTarget_);
+      runtimeTarget_ = nullptr;
+    }
+    if (instance_) {
+      page_->unregisterInstance(*instance_);
+      instance_ = nullptr;
+    }
+  }
+
+  void connect() {
+    ASSERT_FALSE(toPage_) << "Can only connect once in a JSI integration test.";
+    toPage_ = page_->connect(
+        remoteConnections_.make_unique(),
+        {.integrationName = "JsiIntegrationTest"});
+
+    // We'll always get an onDisconnect call when we tear
+    // down the test. Expect it in order to satisfy the strict mock.
+    EXPECT_CALL(*remoteConnections_[0], onDisconnect());
+  }
+
+  void reload() {
+    if (runtimeTarget_) {
+      ASSERT_TRUE(instance_);
+      instance_->unregisterRuntime(*runtimeTarget_);
+      runtimeTarget_ = nullptr;
+    }
+    if (instance_) {
+      page_->unregisterInstance(*instance_);
+      instance_ = nullptr;
+    }
+    instance_ = &page_->registerInstance(instanceTargetDelegate_);
+    runtimeTarget_ = &instance_->registerRuntime(
+        engineAdapter_, engineAdapter_.getRuntimeExecutor());
+  }
+
+  MockRemoteConnection& fromPage() {
+    assert(toPage_);
+    return *remoteConnections_[0];
+  }
+
+  VoidExecutor inspectorExecutor_ = [this](auto callback) {
+    immediateExecutor_.add(callback);
+  };
+
+  jsi::Value eval(std::string_view code) {
+    return engineAdapter_.getRuntime().evaluateJavaScript(
+        std::make_shared<jsi::StringBuffer>(std::string(code)), "<eval>");
+  }
+
+  std::shared_ptr<PageTarget> page_ =
+      PageTarget::create(*this, inspectorExecutor_);
+  InstanceTarget* instance_{};
+  RuntimeTarget* runtimeTarget_{};
+
+  MockInstanceTargetDelegate instanceTargetDelegate_;
+  EngineAdapter engineAdapter_;
+
+ private:
+  UniquePtrFactory<StrictMock<MockRemoteConnection>> remoteConnections_;
+
+ protected:
+  // NOTE: Needs to be destroyed before page_.
+  std::unique_ptr<ILocalConnection> toPage_;
+
+ private:
+  // PageTargetDelegate methods
+
+  void onReload(const PageReloadRequest& request) override {
+    (void)request;
+    reload();
+  }
+};
+
+} // namespace
+
+////////////////////////////////////////////////////////////////////////////////
+
+// Some tests are specific to Hermes's CDP capabilities and some are not.
+// We'll use JsiIntegrationHermesTest as a fixture for Hermes-specific tests
+// and typed tests for the engine-agnostic ones.
+
+using JsiIntegrationHermesTest =
+    JsiIntegrationPortableTest<JsiIntegrationTestHermesEngineAdapter>;
+
+/**
+ * The list of engine adapters for which engine-agnostic tests should pass.
+ */
+using AllEngines = Types<
+    JsiIntegrationTestHermesEngineAdapter,
+    JsiIntegrationTestGenericEngineAdapter>;
+
+TYPED_TEST_SUITE(JsiIntegrationPortableTest, AllEngines);
+
+////////////////////////////////////////////////////////////////////////////////
+
+TYPED_TEST(JsiIntegrationPortableTest, ConnectWithoutCrashing) {
+  this->connect();
+}
+
+TYPED_TEST(JsiIntegrationPortableTest, ErrorOnUnknownMethod) {
+  this->connect();
+
+  EXPECT_CALL(
+      this->fromPage(),
+      onMessage(JsonParsed(
+          AllOf(AtJsonPtr("/id", 1), AtJsonPtr("/error/code", -32601)))))
+      .RetiresOnSaturation();
+
+  this->toPage_->sendMessage(R"({
+                                 "id": 1,
+                                 "method": "Foobar.unknownMethod"
+                               })");
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+TEST_F(JsiIntegrationHermesTest, EvaluateExpression) {
+  connect();
+
+  EXPECT_CALL(fromPage(), onMessage(JsonEq(R"({
+                                             "id": 1,
+                                             "result": {
+                                               "result": {
+                                                 "type": "number",
+                                                 "value": 42
+                                               }
+                                              }
+                                            })")));
+  toPage_->sendMessage(R"({
+                           "id": 1,
+                           "method": "Runtime.evaluate",
+                           "params": {"expression": "42"}
+                         })");
+}
+
+TEST_F(JsiIntegrationHermesTest, ExecutionContextNotifications) {
+  connect();
+
+  InSequence s;
+
+  // NOTE: This is the wrong sequence of responses from Hermes - the
+  // notification should come before the method response.
+  EXPECT_CALL(fromPage(), onMessage(JsonEq(R"({
+                                             "id": 1,
+                                             "result": {}
+                                            })")));
+  EXPECT_CALL(
+      fromPage(),
+      onMessage(JsonParsed(
+          AllOf(AtJsonPtr("/method", Eq("Runtime.executionContextCreated"))))))
+      .RetiresOnSaturation();
+
+  toPage_->sendMessage(R"({
+                           "id": 1,
+                           "method": "Runtime.enable"
+                         })");
+
+  // NOTE: Missing a Runtime.executionContextDestroyed notification here.
+
+  EXPECT_CALL(fromPage(), onMessage(JsonEq(R"({
+                                               "method": "Runtime.executionContextsCleared"
+                                             })")))
+      .RetiresOnSaturation();
+  EXPECT_CALL(
+      fromPage(),
+      onMessage(JsonParsed(
+          AllOf(AtJsonPtr("/method", Eq("Runtime.executionContextCreated"))))))
+      .RetiresOnSaturation();
+  // Simulate a reload triggered by the app (not by the debugger).
+  reload();
+
+  // NOTE: Missing a Runtime.executionContextDestroyed notification here.
+
+  EXPECT_CALL(fromPage(), onMessage(JsonEq(R"({
+                                               "method": "Runtime.executionContextsCleared"
+                                             })")))
+      .RetiresOnSaturation();
+  EXPECT_CALL(
+      fromPage(),
+      onMessage(JsonParsed(
+          AllOf(AtJsonPtr("/method", Eq("Runtime.executionContextCreated"))))))
+      .RetiresOnSaturation();
+  EXPECT_CALL(fromPage(), onMessage(JsonEq(R"({
+                                               "id": 2,
+                                               "result": {}
+                                             })")))
+      .RetiresOnSaturation();
+  toPage_->sendMessage(R"({
+                           "id": 2,
+                           "method": "Page.reload"
+                         })");
+}
+
+} // namespace facebook::react::jsinspector_modern
diff --git a/packages/react-native/ReactCommon/jsinspector-modern/tests/engines/JsiIntegrationTestGenericEngineAdapter.cpp b/packages/react-native/ReactCommon/jsinspector-modern/tests/engines/JsiIntegrationTestGenericEngineAdapter.cpp
new file mode 100644
index 00000000000..2ea6f7cdb43
--- /dev/null
+++ b/packages/react-native/ReactCommon/jsinspector-modern/tests/engines/JsiIntegrationTestGenericEngineAdapter.cpp
@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <jsinspector-modern/FallbackRuntimeAgentDelegate.h>
+
+#include <folly/executors/QueuedImmediateExecutor.h>
+#include <hermes/hermes.h>
+
+#include "JsiIntegrationTestGenericEngineAdapter.h"
+
+using facebook::hermes::makeHermesRuntime;
+
+namespace facebook::react::jsinspector_modern {
+
+JsiIntegrationTestGenericEngineAdapter::JsiIntegrationTestGenericEngineAdapter(
+    folly::Executor& jsExecutor)
+    : runtime_{hermes::makeHermesRuntime()}, jsExecutor_{jsExecutor} {}
+
+std::unique_ptr<RuntimeAgentDelegate>
+JsiIntegrationTestGenericEngineAdapter::createAgentDelegate(
+    FrontendChannel frontendChannel,
+    SessionState& sessionState) {
+  return std::unique_ptr<jsinspector_modern::RuntimeAgentDelegate>(
+      new FallbackRuntimeAgentDelegate(
+          frontendChannel,
+          sessionState,
+          "Generic engine (" + runtime_->description() + ")"));
+}
+
+jsi::Runtime& JsiIntegrationTestGenericEngineAdapter::getRuntime()
+    const noexcept {
+  return *runtime_;
+}
+
+RuntimeExecutor JsiIntegrationTestGenericEngineAdapter::getRuntimeExecutor()
+    const noexcept {
+  return [&jsExecutor = jsExecutor_, &runtime = getRuntime()](auto fn) {
+    jsExecutor.add([fn, &runtime]() { fn(runtime); });
+  };
+}
+
+} // namespace facebook::react::jsinspector_modern
diff --git a/packages/react-native/ReactCommon/jsinspector-modern/tests/engines/JsiIntegrationTestGenericEngineAdapter.h b/packages/react-native/ReactCommon/jsinspector-modern/tests/engines/JsiIntegrationTestGenericEngineAdapter.h
new file mode 100644
index 00000000000..83ea5952acb
--- /dev/null
+++ b/packages/react-native/ReactCommon/jsinspector-modern/tests/engines/JsiIntegrationTestGenericEngineAdapter.h
@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <jsinspector-modern/RuntimeTarget.h>
+
+#include <folly/executors/QueuedImmediateExecutor.h>
+#include <jsi/jsi.h>
+
+#include <memory>
+
+namespace facebook::react::jsinspector_modern {
+
+/**
+ * An engine adapter for JsiIntegrationTest that represents a generic
+ * JSI-compatible engine, with no engine-specific CDP support. Uses Hermes under
+ * the hood, without Hermes's CDP support.
+ */
+class JsiIntegrationTestGenericEngineAdapter : public RuntimeTargetDelegate {
+ public:
+  explicit JsiIntegrationTestGenericEngineAdapter(folly::Executor& jsExecutor);
+
+  virtual std::unique_ptr<RuntimeAgentDelegate> createAgentDelegate(
+      FrontendChannel frontendChannel,
+      SessionState& sessionState) override;
+
+  jsi::Runtime& getRuntime() const noexcept;
+
+  RuntimeExecutor getRuntimeExecutor() const noexcept;
+
+ private:
+  std::unique_ptr<jsi::Runtime> runtime_;
+  folly::Executor& jsExecutor_;
+};
+
+} // namespace facebook::react::jsinspector_modern
diff --git a/packages/react-native/ReactCommon/jsinspector-modern/tests/engines/JsiIntegrationTestHermesEngineAdapter.cpp b/packages/react-native/ReactCommon/jsinspector-modern/tests/engines/JsiIntegrationTestHermesEngineAdapter.cpp
new file mode 100644
index 00000000000..5caa9980a94
--- /dev/null
+++ b/packages/react-native/ReactCommon/jsinspector-modern/tests/engines/JsiIntegrationTestHermesEngineAdapter.cpp
@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <folly/executors/QueuedImmediateExecutor.h>
+
+#include <hermes/inspector-modern/chrome/HermesRuntimeAgentDelegate.h>
+
+#include "JsiIntegrationTestHermesEngineAdapter.h"
+
+using facebook::hermes::makeHermesRuntime;
+
+namespace facebook::react::jsinspector_modern {
+
+JsiIntegrationTestHermesEngineAdapter::JsiIntegrationTestHermesEngineAdapter(
+    folly::Executor& jsExecutor)
+    : runtime_{hermes::makeHermesRuntime()}, jsExecutor_{jsExecutor} {}
+
+std::unique_ptr<RuntimeAgentDelegate>
+JsiIntegrationTestHermesEngineAdapter::createAgentDelegate(
+    FrontendChannel frontendChannel,
+    SessionState& sessionState) {
+  return std::unique_ptr<jsinspector_modern::RuntimeAgentDelegate>(
+      new HermesRuntimeAgentDelegate(
+          frontendChannel, sessionState, runtime_, getRuntimeExecutor()));
+}
+
+jsi::Runtime& JsiIntegrationTestHermesEngineAdapter::getRuntime()
+    const noexcept {
+  return *runtime_;
+}
+
+RuntimeExecutor JsiIntegrationTestHermesEngineAdapter::getRuntimeExecutor()
+    const noexcept {
+  auto& jsExecutor = jsExecutor_;
+  return [runtimeWeak = std::weak_ptr(runtime_), &jsExecutor](auto fn) {
+    jsExecutor.add([runtimeWeak, fn]() {
+      auto runtime = runtimeWeak.lock();
+      if (!runtime) {
+        return;
+      }
+      fn(*runtime);
+    });
+  };
+}
+
+} // namespace facebook::react::jsinspector_modern
diff --git a/packages/react-native/ReactCommon/jsinspector-modern/tests/engines/JsiIntegrationTestHermesEngineAdapter.h b/packages/react-native/ReactCommon/jsinspector-modern/tests/engines/JsiIntegrationTestHermesEngineAdapter.h
new file mode 100644
index 00000000000..bffce0db32d
--- /dev/null
+++ b/packages/react-native/ReactCommon/jsinspector-modern/tests/engines/JsiIntegrationTestHermesEngineAdapter.h
@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <jsinspector-modern/RuntimeTarget.h>
+
+#include <folly/executors/QueuedImmediateExecutor.h>
+#include <hermes/hermes.h>
+#include <jsi/jsi.h>
+
+#include <memory>
+
+namespace facebook::react::jsinspector_modern {
+
+/**
+ * An engine adapter for JsiIntegrationTest that uses Hermes (and Hermes's
+ * CDP support).
+ */
+class JsiIntegrationTestHermesEngineAdapter : public RuntimeTargetDelegate {
+ public:
+  explicit JsiIntegrationTestHermesEngineAdapter(folly::Executor& jsExecutor);
+
+  virtual std::unique_ptr<RuntimeAgentDelegate> createAgentDelegate(
+      FrontendChannel frontendChannel,
+      SessionState& sessionState) override;
+
+  jsi::Runtime& getRuntime() const noexcept;
+
+  RuntimeExecutor getRuntimeExecutor() const noexcept;
+
+ private:
+  std::shared_ptr<facebook::hermes::HermesRuntime> runtime_;
+  folly::Executor& jsExecutor_;
+};
+
+} // namespace facebook::react::jsinspector_modern